Many communications have timing schemes or timing structures for managing communications between devices. Time can be defined in any number of units and subunits where the communication equipment applies the timing to transmission and reception. For example, some systems divide time into at least frames, subframes, timeslots, and symbol times.
The frequency spectrum used by a particular communication may be licensed or unlicensed. Licensed frequency spectrum (frequency band) is licensed to a system operator by a government agency, such as the Federal Communications Commission (FCC). An example of such licensed spectrum includes frequency bands used for cellular communication. An unlicensed frequency band is any portion of frequency spectrum that does not require a license from the government agency to communicate with the unlicensed frequency band. Equipment operating within the unlicensed band, however, typically must adhere to regulations and/or communication standards. An example of an unlicensed frequency spectrum includes frequency bands used for Institute of Electrical and Electronics Engineers (IEEE) 802.11 communication.
In some communication systems, an eNB (evolved Node B, eNodeB, base station, etc.) uses a licensed frequency band for control signaling and uses the unlicensed frequency band for data transmission to a user equipment (UE) device. The service area provided using the licensed frequency band is sometimes referred to as a primary cell (Pcell) and the service area provided using the unlicensed frequency band is sometimes referred to as a secondary cell (Scell). Although the timing structure (frames, subframes, symbols, etc.) used in the Pcell are applied within Scell, the UE device may not have timing information sufficient to communicate in the unlicensed frequency band. The eNB transmits Discovery Reference Signals (DRS) within the Scell which provides synchronization/timing information to the UE device.